Imaging human irises for biometric identification purposes usually requires that the subject's iris be illuminated in near-infrared (NIR) wavelengths just beyond those of visible red light. Bright light at such wavelengths is not visible and does not trigger an aversion response, such as pupil narrowing, blinking or averted gaze. Despite humans being relatively unaware of such illumination, it passes through the cornea and lens of the eye, where it is magnified by a varying amount, dependent primarily on the pupil size, and focused on the retina. Optical gain of a retina with a dilated iris can increase the incident optical power on the central high-acuity cells of a fovea by a factor of 100×. NIR light pulses above a certain intensity or total energy can damage the retina, particularly the cells of the fovea which provide acute central vision. US and international eye safety regulations strongly constrain the time-energy profile of deliberate NIR radiation that can reach an unprotected eye ball.